El Niño and the Indian Monsoon

El Niño is the warm phase of the El Niño-Southern Oscillation (ENSO), a coupled ocean-atmosphere phenomenon in the tropical Pacific. It involves sustained, large-scale warming of the central and eastern equatorial Pacific, accompanied by changes in trade winds, atmospheric pressure and tropical rainfall patterns.

Ocean-atmosphere process

El Niño begins in the tropical Pacific but affects distant regions through changes in large-scale atmospheric circulation, known as teleconnections.

• Under normal conditions, easterly trade winds push warm surface water towards the western Pacific, where rising warm, moist air supports strong convection.
• During El Niño, the trade winds weaken and warm surface water and associated convection shift eastwards towards the central and eastern Pacific.
• This shift alters the east-west Walker circulation and redistributes zones of rising and descending air across the tropics.
• The Southern Oscillation is the associated atmospheric pressure fluctuation; together, the oceanic and atmospheric components constitute ENSO.

Influence on the Indian summer monsoon

El Niño tends to weaken the Indian summer monsoon, but the relationship is probabilistic rather than automatic.

• The eastward displacement of Pacific convection can produce circulation anomalies that favour descending air over parts of the Indian region, suppressing cloud formation and rainfall.
• Changes in tropical pressure and wind patterns can weaken monsoon circulation and moisture transport towards the Indian subcontinent.
• The result may be below-normal or uneven seasonal rainfall and longer dry spells during the southwest monsoon season.
• Every El Niño does not cause a drought, because Indian Ocean conditions, including the Indian Ocean Dipole, and intra-seasonal monsoon variability can reinforce or offset its influence.

Transmission to agricultural production

The agricultural effect operates mainly through the timing, amount and spatial distribution of monsoon rainfall, with rainfed farming being especially exposed.

• Weak or delayed early-season rainfall can postpone kharif sowing and reduce the area planted.
• Deficient rainfall lowers soil moisture and can impair germination, crop growth and yields, especially where irrigation is limited.
• Long dry spells during critical crop stages can reduce output even when total seasonal rainfall appears less deficient.
• Poor monsoon rainfall reduces inflows into reservoirs and groundwater recharge, affecting irrigation for the remaining kharif season and subsequent rabi crops.
• The final production impact varies across regions and crops according to irrigation coverage, rainfall distribution, crop choice and farm-level adaptation.
• A widespread fall in agricultural output can reduce rural incomes, tighten food supplies and create upward pressure on food prices.

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